COPD is associated with significant morbidity including substantial daytime fatigue exertional intolerance and ventilatory impairment, which hits is a nadir in the morning. Although COPD related impairments in ventilation are considered to play a role for sleep disturbances, the mechanisms of how COPD specific alterations in ventilation affects sleep, particularly in patients without sleep apnea, remain unclear. We hypothesize that in patients with COPD sleep attenuates compensatory mechanisms needed to defend ventilation leading to periods of dynamic hyperinflation and hypoventilation resulting in sleep disturbances. In the current proposal, we use a novel diagnostic flow-sensor for quantifying ventilation during sleep to detect specific mechanisms accountable for ventilatory decompensation during sleep and to determine the prevalence of COPD related sleep disordered breathing episodes in a community recruited cohort of individuals with COPD. While long-term oxygen treatment significantly improved mortality, studies examining the effects of nocturnal oxygen administration in patients with borderline hypoxia on clinical outcomes and sleep quality in COPD have been inconclusive. Our preliminary data demonstrate that oxygen administration during sleep reduces neuromuscular drive to the upper airway and aggravates ventilatory decompensation in patients with COPD. Thus, although oxygen may help to relieve daytime symptoms, nocturnal use of oxygen may in fact be harmful in patients with COPD as it exaggerates impairments in ventilation during sleep. In contrast, the PI recently established that nasal insufflation of room air (NI) effectively stabilizes breathing during sleep in patients with inspiratory flow limitation. Moreover, we now demonstrate that, in contrast to nocturnal oxygen, this novel approach can lower hypercapnia by mitigating the mechanisms accountable for ventilatory failure during sleep. The current proposal will extend our knowledge of the pathophysiologic mechanisms for the development of sleep disordered breathing in patients with COPD. It will also change current paradigms for diagnosing and treating COPD patients. This shift will be built through: (1) the establishment of a high prevalence of COPD specific sleep disordered breathing episodes independent of obstructive sleep apnea (OSA) (SA1),(2) the determination of the underlying mechanisms for dynamic hyperinflation and hypoventilation during sleep in COPD (SA2), and (3) the demonstration that NI improves sleep and breathing better than supplemental oxygen in COPD (SA3).